Seiichiro Koda

Crystal structure and ferroelectric properties of rare-earth substituted BiFeO3 thin films

The influence of ion modification using rare-earth cations on crystal structures, along with the insulating and ferroelectric properties of BiFeO3 (BFO) thin films was investigated. Rare-earth-substituted BFO films with chemical compositions of (Bi1.00−xREx)Fe1.00O3 (x=0–0.15, RE=La and Nd) were fabricated on (111)Pt∕TiO2∕SiO2∕(100)Si substrates using a chemical solution deposition technique. A crystalline phase of rhombohedral BFO was obtained by heat treatment in a N2 atmosphere at 500°C for 5min. The crystal anisotropy and the Curie temperature of BFO were degraded continuously with increasing contents of La3+ or Nd3+ cations. Ion modification using La3+ and Nd3+ cations up to x=0.05 lowered the leakage current density of the BFO film at room temperature from approximately 10−3 down to 10−6A∕cm2. A polarization (P)-electrical field (E) hysteresis loop measured at 10K revealed that the intrinsic remanent polarization of La3+- and Nd3+-substituted BFO films with x=0.05 (44 and 51μC∕cm2, respectively) was...

Size reduction of gold particles in aqueous solution by pulsed laser irradiation

When the gold particles produced by the chemical reduction of hydrogen chloroaurate solution were irradiated by the second harmonic of a pulsed Nd:Yag laser (532 nm), their diameter was reduced from more than several deca-nm to less than 20 nm. At the same time, the shape of the particles, originally nonspherical, became spherical. This phenomenon was limited to pulsed laser, and is caused by the heating of the particles within the very short time of laser irradiation; the very large absorption cross section of the particles at the plasmon absorption and the thermal insulation of the irradiated particles in water should be responsible.

Ion Modification for Improvement of Insulating and Ferroelectric Properties of BiFeO3 Thin Films Fabricated by Chemical Solution Deposition

Ion modification techniques for improving the insulating and ferroelectric properties of BiFeO3 (BFO) thin films are reported. Rare-earth-substituted BFO films with chemical compositions of Bi1.00-xRExFe1.00O3 [RE = La and Nd] were fabricated on (111)Pt/TiO2/SiO2/(100)Si substrates using a chemical solution deposition technique. Well-saturated P-E curves were obtained for La3+- and Nd3+-substituted BFO films, while the curve of a nonsubstituted BFO film was distorted due to the leakage current. Remanent polarization (Pr) values measured at 10 K were respectively 44 and 51 µC/cm2, for La3+- and Nd3+-substituted BFO films, which are significantly superior to conventional Pb-free ferroelectrics.

Emission and energy transfer of triplet difluoromethylene produced in the reaction of oxygen atoms with tetrafluoroethylene

Abstract Structured emission spectra have been observed in the wavelength range 470–720 nm from the reaction of oxygen atoms with tetrafluoroethylene. The emissions is tentatively assigned to the CF 2 ( 3 B 1 ) → CF 2 ( 1 A 1 ) phosphorescence transition. The excited singlet CF 2 ( 1 B 1 ) is also formed through the triplet—triplet annihilation from the triplet CF 2 .

Solid‐state ultraviolet tunable laser: A Ce3+ doped LiYF4 crystal

A large gain and a wide tunability have been achieved over the Ce3+ (5d‐4f) transition in a LiYF4 crystal. A gain coefficient in excess of 180 cm−1 and a superradiant beam of 2.5 mrad divergence are observed at the laser transition, 325.2 nm, when the crystal is optically excited either at 193 or at 248 nm. Gain measurements indicate that the laser is tunable over a wavelength range of more than 10 nm.

Analysis for crystal structure of Bi(Fe,Sc)O3 thin films and their electrical properties

Thin films of Bi(Fe1−xScx)O3 (BFSO) system were fabricated on (111)Pt∕TiO2∕SiO2∕(100)Si substrates by chemical solution deposition to improve the electrical resistivity by substituting electrically unstable Fe3+ cations for stable Sc3+ cations. A single phase of perovskite was obtained in the range of x=0–0.30, in which selective replacement of Fe3+ and Sc3+ was confirmed in x=0–0.15 by using Raman measurement. The leakage current density of the BFSO films was reduced by increasing x. A well-saturated polarization–electric field hysteresis loop was obtained for BFSO films with x=0.15, showing remanent polarization of approximately 35μC∕cm2.

A study of inhibition effects for silane combustion by additive gases

Abstract By use of an opposed jet diffusion flame technique, the effect of addition of a variety of gases to the silane combustion which proceeds through the following two gross reactions, SiH 4 + O 2 → SiO 2 (s) + 2H 2 (1) and SiH 4 + 2O 2 → SiO 2 (s) + 2H 2 O (2), has been studied. On the basis of their inhibition effect, the additive gases could be classified into three groups. The first group, which included N 2 , CO 2 , and CF 4 , showed almost no inhibition effect. On the other hand, the addition of the second group gases such as CF 3 Br and CF 3 H changed the color of the flame and lowered the flame temperature. At the same time, a large production of H 2 was observed in the exhaust gas. Ignition and extinction properties, however, did not vary in the presence of these gases. It was concluded that the progress of the gross reaction (2) was considerably retarded by the second group gases. Ethylene, as a third group gas, strongly inhibited the ignition and also made it difficult to maintain the flame of a low silane content. Ethylene must interfere in the progress of the gross reaction (1) due to its high reactivity against atomic and radical species. These additive effects are discussed on the basis of a silane combustion mechanism where the important chain carrier is the SiH 3 radical.

Microwave kinetic spectroscopy of reaction intermediates: O+ethylene reaction at low pressure

A microwave spectroscopic method has been developed to study elementary reactions in real time through in situ observation of rotational spectra of reaction intermediates such as free radicals with lifetime as short as 1 ms. This method was applied to the O(3P)+ethylene reaction in order to assess the roles of (a) vinoxy+H and (b) CH3+CHO channels in the initial process. The reaction was initiated by irradiating an N2O/C2H4 mixture containing a trace amount of mercury with the 253.7 nm mercury resonance line, and the time evolution of vinoxy, HCO, and H2CO was followed by measuring their microwave absorption intensities as functions of time. The branching ratio was thus determined to be 0.4±0.1 and 0.5±0.1 for (a) and (b), respectively, at the sample pressure of 30 mTorr. The present result agrees with those obtained by Hunziker et al. [J. Photochem. 17, 377 (1981)] using much higher pressures of samples, but is not compatible with the observation of Buss et al. [J. Photochem. 17, 389 (1981)] that (a) is ...

Dependence of Ferroelectric Properties on Thickness of BiFeO3 Thin Films Fabricated by Chemical Solution Deposition

Bismuth ferrite (BiFeO3) thin films were fabricated by depositing sol–gel solutions on Pt/Ti/SiO2/Si(100) structures. X-ray diffraction (XRD) showed that a polycrystalline phase and also a small fraction of a secondary phase, Bi2Fe4O9, were present in the film. The nonperovskite secondary phase decreased with increasing thickness, which showed the influence of volume effects on the film. Improved leakage current density and enhanced polarization in BiFeO3 films were observed. A 400-nm-thick film showed a leakage current on the order of 10-8 A/cm2 at room temperature. The remanent polarization was approximately 90 µC/cm2 at 80 K and the piezoelectric coefficient d33 was approximately 50 pm/V.

Size reduction of silver particles in aqueous solution by laser irradiation

The effect of pulsed laser irradiation on silver particles in aqueous solution was investigated. The particle size decreased and the size distribution became narrower after irradiation for 15 minutes using third harmonics of a pulsed YAG laser. The number of the aggregated particles also decreased after the irradiation.